when you make a withdrawal from a website (in this case withdrawing from localbitcoins.com) the  cost is not a bitcoin transaction cost the cost is that third party withdrawal cost. and they can ask for any amount they wish regardless of how much it costs them to send you the transaction. there  currently are exchanges that will charge you 0.001BTC for a bitcoin withdrawal just because they can and then they pay 0.000002BTC transaction fee themselves to send you the coins. the difference is their profit.

it depends on the exchange you are using, you have to check out their fees. the fee as I mentioned above is not a network fee. some exchanges are even charging a % of your amount. I remember it was btc-x (coinsbank) that charged about 1%. for instance if you wanted to withdraw 10BTC you should have paid 0.1BTC in fee!